Elastomeric silicone foams are well known and have a variety of uses, including thermal insulation, electrical insulation, flame barrier, cushioning applications, etc. Elastomeric silicone foams have excellent physical properties and in addition to the above uses are suitable and desirable for use in many additional applications. However, there is a problem with elastomeric silicone foam that it is expensive and at 15-25 lb/ft.sup.3, the ability to reduce price is limited by the basic costs of silicone material.
The technical advances necessary to significantly reduce the basic cost of silicone material are not on the horizon, thus it is clear that to immediately reduce the cost of elastomeric silicone foam it is necessary to reduce the density of the foam. Although this may seem to be a simple matter of adding additional blowing agent, etc., it is an aspect of elastomeric silicone foam as presently used that density is not easily lowered. The reasons for this are apparent with a review of silicone foam technology.
U.S. Pat. No. 3,923,705, Smith, discloses that elastomeric silicone foams may be produced with a single reaction that both cross-links to cure the composition as well as produces hydrogen gas to blow the foam. This reaction takes place between a silanol and silicon hydride. Optionally, there can be added a vinyl containing silicone that will simultaneously cross-link through addition with a silicon hydride without gas generation. Obviously, this is a convenient method to produce silicone foam. It is also true, however, that gas generation must be proportional to cross-linking or cure rate and therefore density is difficult to control.
U.S. Pat. No. 4,189,545, Modic, produces silicone foam compositions by adding water. For example, water could be added to a composition of a vinyl containing siloxane, a hydride containing siloxane and platinum to generate gas at a rate only indirectly related to cross-linking rate. The water reacts with hydride containing siloxane to produce hydrogen gas and silanol. Silanol reacts with hydride containing siloxane to cross-link and produce a second molecule of hydrogen gas. A vinyl addition reaction with silicone hydride will cross-link the composition simultaneously. Thus, a major advantage of Modic is that gas is produced without the addition of silanol and with only small amounts of water.
U.S. Pat. No. 4,418,157, Modic, reduces density and strengthens silicone foam by adding a resinous copolymer. U.S. Pat. No. 4,599,367, Baumann, et al., reduces density by using a combination of silanol and water.
There have been two disclosures to date of methods and additives by which the self-blowing characteristics of elastomeric silicone foam is controlled independently of cure. Copending U.S. Pat. Ser. No. 113,292 filed Oct. 26, 1987, and U.S. Pat. Ser. No. 113,023 filed Oct. 26, 1987, add an amine compound or a silica filler with surface nitrogen prior to blowing to lower foam density. It is believed that the presence of these materials accelerates gas formation while delaying cure. Thus, gas formation and cure are optimized to reduce foam density.
It is desirable to develop additional additives to reduce foam density. Such additives should also reduce cell size and improve cell uniformity.
Thus, it is an object of the present invention to develop additives to reduce foam density.
It is a further object of the present invention to develop such an additive that reduces cell size as well as improves cell uniformity.
These and other objects of the present invention are accomplished by means of the disclosure set forth hereinbelow.